1. Field of the Invention
The invention is in the field of push-back storage racks and, more particularly, a low profile push-back storage rack assembly.
2. Background of the Prior Art
Push-back racks exist in the prior art to store palletized loads which are handled by fork trucks from a central aisle. The racks generally extend laterally from both sides of an aisle and may be installed adjacently side by side. The racks themselves generally have vertical posts and lateral cross-members which may be arranged to define at least three-deep compartments or bays which are conveniently referred to respectively as a first bay, a second bay and a third bay. The bays or compartments are suitably sized to accommodate palletized cargo. Typically, the bays are vertically stacked by extending the rack vertically, usually four to six sets of bays high. The limiting factors are the height of the warehouse clear space and the lifting height which can be reached by the fork trucks.
There is at least one pair of rails in each compartment which extend longitudinally throughout at an inclination toward a common loading and unloading side. The rails are spaced apart to accommodate at least two flat pallet carriages or carts of different heights, the higher of the carriages or carts being adapted to roll completely over the lower carriage or cart. Both carts come to rest in the first bay.
This makes it possible to load and unload each compartment or bay from the front of the rack. If the compartments are empty, the carriages roll forwardly along the inclined rails to rest against a stop. Then a pallet can be placed on the higher carriage or cart. A fork-lift truck then lifts another pallet somewhat above the level of the loading surface of the lower cart. The pallet held by the fork-lift truck is pushed against the side of the pallet which had previously been loaded on the first cart. As the fork-lift moves forward, the second pallet pushes the first loaded pallet back to the middle or intermediate bay and the pallet and load on the forks are moved into the first bay and lowered onto the second can. Now the first and second bays contain loaded pallets.
A third pallet can be introduced by lifting it somewhat above the level of the pair of rails and then pushing it into the first compartment whereby the side of the third pallet or its load pushes against the side of the second loaded pallet. As the fork-lift truck pushes the third pallet into the first bay, the other two previously loaded pallets roll on their cans back into the second and third bays, and the third pallet is lowered onto the rails. Since the third pallet now occupies the first bay, it prevents the loaded cans from moving forward, and storage is provided for all three pallets within the rack. Unloading is accomplished in reverse order by removing the pallet from the first bay which allows the pallet in the second bay to roll on its cart to the first bay and the pallet in the third bay to roll on its cart to the second bay. Thus the compartments are located sequentially in order and unloaded in reverse order. Additional rails can be added with additional carts in various combinations to provide for more than three compartments deep with more than two cans.
In order to function, the prior art carts must be configured so that the higher first cart can freely roll completely over the lower second cart so that they can both rest one above the other in the first compartment to be loaded and unloaded. The carts, their wheel structure and the rails must be durable and capable of handling heavy pallet loads. Additional compartments with another set of supporting cross-members, rails and carts are stacked directly over the lower compartments or bays. The height of the carts in the compartment below affects head space which is required to load and unload pallets. Head space may be considered the clear vertical space between the top surface of the highest cart in the first bay and the undersurface of the cross-members immediately above the higher cart.
Head space is important in several ways. There must be enough space provided to accommodate the largest load to be manipulated by the fork truck within the confines of the first compartment. The fork-lift operator must be able to lift and place the pallets on the carts without the load coming into contact with the cross-members above. This necessitates elevating the cross-members of the second story row of compartments a certain height above the first row of compartments and similarly placing the cross-members of the third vertically stacked row of compartments above the height of the highest cart positioned thereunder. More elevation is required the greater the height of the carts stacked in the front bay. The effect is cumulative.
Fork-lift trucks are limited in their vertical lifting elevation. The forks can go only so high. The number of vertically stacked rows of compartments can be limited because the fork-lift may not be able to raise the pallet high enough to clear the highest cart in the uppermost first compartment. This can lead to a loss of a whole row of compartments, depending upon how much additional vertical height is occupied by each set of stacked carts. In addition to that problem, the warehouse itself may have girders, piping or other obstructions which limit the overall maximum vertical height, which itself can limit the number of rows that can be vertically stacked if the carts are stacked too high above the rails.